Bitcoin mining “guzzles energy,” Wired declares. The process “uses more electricity than Iceland,” Digital Trends says. It “consumes more electricity a year than Ireland,” warns The Guardian.

Forget for a moment the sudden mass alarm over how much electricity bitcoin mining uses—for a layperson, the very fact that it requires electricity to mine a digital asset may be confusing. Here’s how it all works.

How does bitcoin mining work?

Bitcoin runs on blockchain, a public, permanent, decentralized ledger where all bitcoin transactions are recorded in bundles of multiple transactions, called “blocks.” The blocks are added to the chain (hence “blockchain”) by “miners” who mine, or verify, the blocks.

Mining requires large, expensive machines that compete to solve complicated math problems in real time. The computations get continuously harder, and so the machines are getting more advanced to keep up, and more expensive as a result. The best ones cost thousands of dollars.

Mining doesn’t require the human being to physically sit and solve those formulas—you can plug it in, download the proper mining software, and let it run; the machine does the work.

The process is called “mining” because, like the mining of a physical resource such as oil or gold, there is a finite supply: the amount of bitcoins is capped at 21 million. When a miner verifies a block, they receive a tiny amount of new bitcoins as a reward, and that is the only way new bitcoins are created; they cannot be duplicated. So far, 16.8 million bitcoins have been mined, and at the current rate we won’t hit the 21 million cap for over 100 years.

The amount of bitcoin that miners receive as reward also gets halved every four years. That last happened in 2016 and has happened just twice in bitcoin’s history. The current reward is 12.5 bitcoins per block mined.

Thus the increasing amount of power required to mine cryptocurrency is by design: there’s more competition than ever to mine blocks, so the process needs to be competitive to keep the number of newly created bitcoins constant. As more miners join the network, the difficulty of mining increases.

While it is possible to mine bitcoin from a standard personal computer without advanced equipment, as part of a mining pool, it isn’t really worth the effort. Yahoo Finance’s Jared Blikre tried mining bitcoin from his own laptop and found that at his current computing power, it would take him 1,197 years to mine 1 bitcoin. It’s simply too inefficient without an ASIC rig.

It isn’t just bitcoin that uses mining: Ethereum, a blockchain for smart contracts, works the same way, and Ethereum miners are rewarded in ether coins.

Is the energy consumption a cause for alarm?

Much of the sudden concern around the amount of energy that mining consumes was stoked by a new “bitcoin energy consumption index” from Digiconomist in December. The index uses the monthly total of terrawatts used to project annual terrawatts used, and shows no end in sight to the upward trend. It currently projects global bitcoin mining at 39 terrawatts per year. The index also compares the numbers to energy use by other countries (bitcoin mining is currently using 60% the amount of energy that the entire Czech Republic uses) and to other payment networks (bitcoin mining energy usage blows the Visa payment network out of the water).

“It’s a complex issue,” says Brian Hoffman, founder of OpenBazaar, a peer-to-peer marketplace where buyers pay in bitcoin. “Certainly mining consumes massive amounts of energy which may harm the environment depending on how it’s sourced. But I think energy must be expended in order to be rewarded with value, so this is not wasteful. Everything we do is about expending energy for value, from mowing the lawn to cooking a meal. If no energy is consumed, no value is created.”

If the price of bitcoin rises to new heights in 2018, expect the debate over mining to rage on.

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Daniel Roberts covers bitcoin and blockchain at Yahoo Finance. Follow him on Twitter at @readDanwrite.